Recently published experiments suggest that in the B\lymphocyte, membrane-bound immunoglobulin (mIg) is associated with other plasma membrane proteins as well as with the cytoskeleton, through actin. Our preliminary results show that some of the B-cell actin-associated proteins are phosphoproteins. It appears that, in some cases, the level of protein phosphorylation can be modulated in vitro by reacting B\cells with anti-mIg antibodies. The objective of this proposal is to elucidate the molecular nature of the mIg interactions and to determine how they are influenced when mIg is either cross-linked or capped as a result of anti-Ig reagents binding to B-cell surfaces. Our approach will be biochemically and immunochemically oriented, employing standard techniques of protein chemistry. We will make extensive use of the method of myosin affinity chromatography. This work will improve our understanding of how surface proteins on or within the plasma membrane can interact with each other and the cytoskeleton, in the control of normal cell function.